Functional Programming In JavaScript — With Practical Examples (Part 1) Functional Programming(FP) can change the way you program for the better. If you do a quick web search for functors, you will find articles that will bombard you with terms such as: morphism and categories. Let's write a function that duplicates every item in an array (e.g. “Monads” apply a function that returns a wrapped value. [1,2,3]--> [1,1,2,2,3,3]). MayBe Functors. Slowly, it begins to make sense. A Map to Success: Functors in Javascript by Kevin Welcher (a functor is just an object that implements map(), so monads are functors that implement a couple of extra things on top). By Daniel Weiner, Software Engineer, Breakthrough Technologies In this article I'll talk about a concept that is prevalent in functional programming: monads. Monads. You wouldn’t claim to ‘understand’ monads, but you can see how using Maybe might save a lot of effort. A discussion on functors can easily get very formal and theoretical. Their definitions are frightening, too: Functor The type signature of an array monad is. To be considered a monad the structure has to provide three components: type constructor — a feature that creates a monadic type for the underlying type. That is not all. The bad news is arrays are functors, so you can't escape them. This is part 3 in a series on Functional Programming in javascript. The good news is arrays are monads, so when you get into this situation of … Monads If you do I know, those words can be frightening. M: [T] -> [T] where T is a given type. Functors and monads can provide additional utility and types when working with JavaScript. We have to put some type restriction on the function passed it … Pure JavaScript – Christian Johansen will show you how you can significantly up your game by leaving loops behind and embracing functions … Totally valid, you could do that. Functional programming patterns for the non-mathematician – Learn about practical use cases for functors, applicatives, and monads. A MayBe functor is one that lets us implement a map function in a different way. In the end they are containers which serve a specific purpose and follow a series of rules. But monads do. We start off by creating a constructor that stores a value: const MayBe = function(val) { this.value = val; } MayBe.of = function(val) { return new MayBe(val); } But functors do not place any such restriction. Let's first try with map: According to me, Promises are Functors, Applicative Functors and Monads since they obey the functor and monads laws. In this article, we’ll look at how to pipe functions and functors with JavaScript. Giving a definition of monad is somewhat tedious and requires a bit of theory, so we are first going to build an intuition for them through examples. Array Monad. For Promises to be an instance of Functor we must define an fmap function (a -> b) - f a -> f b for Promises and fmap shall pass the Functor laws. Monads wrap types giving them additional behavior like the automatic propagation of empty value (Maybe monad) or simplifying asynchronous code (Continuation monad). Part 1: The Unit; Part 2: The Monoid; Part 4: The art of chaining different monads; After discovering the Unit and the Monoid, it's time to talk about Functors and Monads. We'll learn about JavaScript promises as well, and I'll talk about how we can learn from functional programming when developing in JavaScript. functors: you apply a function to a wrapped value using fmap or <$> applicatives: you apply a wrapped function to a wrapped value using <*> monads: you apply a function that returns a wrapped value, to a wrapped value using >>= Graphic That is why map is a functor but not a monad. 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